Clutch hydraulic control device, in particular for motor car

ABSTRACT

The invention concerns a device comprising a shift cylinder with a cylinder body ( 17 ) bearing a first sleeve ( 54 ) for guiding a second sleeve ( 42 ) enclosing an axially mobile piston ( 21 ) with an intervening piston seal between the second sleeve ( 42 ) and the piston ( 21 ) and a secondary seal ( 59 ) between the body ( 17 ) and the second sleeve ( 42 ) penetrating into the hydraulic chamber. The invention is applicable to motor vehicles.

International patent application Ser. No. PCT/FR99/01355, publicationNo. WO99/64758

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for the hydraulic control of aclutch, especially for motor vehicles, comprising at least one emitteror receiver cylinder having a piston.

More particularly, the invention relates to a hydraulic control devicefor a motor vehicle clutch including at least one control cylinder, ofthe type in which the cylinder comprises a substantially tubularcylinder body in which there slides axially a piston which, through afront transverse face, bounds a hydraulic chamber, and which is incooperation through a rear transverse face with a piston rod, wherein anaperture for connection of a pipe or a duct is open into the hydraulicchamber, and wherein the cylinder body is made of mouldable materialsuch as plastics material.

Such a device is described for example in the document DE-U-2951 6488.

2. Description of the Related Art

In the latter, the piston is part of an assembly which includes ametallic piston skirt.

More precisely, the piston skirt has at its front end a projectingelement on which the piston is formed by applied moulding. The skirtserves as a receptacle for two half shells which are so configured as toreceive the head of the rod of the piston.

In addition, the piston carries a piston seal which is adapted tocooperate with a metallic guide sleeve mounted in the internal bore ofthe cylinder body and bounding the hydraulic chamber, while the cylinderbody carries a secondary seal which is adapted to cooperate with thepiston skirt. The cylinder body is for this purpose stepped internallyin diameter, so that it has, at its rear end, an enlarged cross sectionwhereby it can contain the secondary seal within it. A securing skirt ismounted in this larger section so as to retain the secondary seal.

Such a solution, which calls for a large number of components, isrelatively costly and necessitates the presence of a dynamic piston sealcarried by the piston and cooperating with the guide sleeve fixed to thecylinder body.

An object of the present invention is to overcome these drawbacks in asimple and inexpensive way.

SUMMARY OF THE INVENTION

According to the invention, a hydraulic control device of the typedescribed above is characterized in that the piston is so configured asto receive the head of the piston rod, in that the piston is surroundedby the piston skirt, in that the piston seal is interposed operativelybetween the outer periphery of the piston and the inner periphery of thepiston skirt, and in that the piston skirt penetrates into the hydraulicchamber.

Thanks to the invention, the guide sleeve of the prior art iseliminated, and the piston skirt penetrates into the hydraulic chamber.The piston and the piston skirt are concentric and coaxial components,and they constitute a unit in the form of a sub-assembly which can behandled and transported.

It should be noted that the manufacturing cost of the outer surface ofthe piston skirt is less than the manufacturing cost of the innersurface of the guide sleeve in the prior art, the said outer surfacebeing in cooperation with the secondary seal of the dynamic type. Theimmobilizing skirt is elongated axially and is a good guide for thepiston skirt. The internal bore of the said skirt extends the internalbore of the cylinder body.

The piston seal has a simplified form, and acts statically between thepiston and the piston skirt. In one embodiment, the piston seal consistsof an O-ring seal.

The piston skirt has a simple and inexpensive tubular form. This skirtdoes not have a base portion.

Preferably, the piston is of plastics material such that the seating forthe head of the piston rod can easily be formed by moulding.

Preferably, the cylinder body has an abutment which serves to centre thespring which acts between the base of the body of the cylinder and thepiston.

The front face of the piston is arranged to come into contact with thisabutment.

Thus the piston skirt only undergoes weak forces when the piston is inits retracted position.

In one embodiment, the piston has a posterior axial fixing groove intowhich at least one deformation of the piston skirt penetrates.

The deformation of the skirt, which constitutes a projecting element,penetrates, for example by insertion, into the groove in such a way thatthe piston skirt is fixed axially to the piston. For example the pistonskirt has lugs or pegs penetrating into the groove of the piston.

The skirt can then be snap-fitted on the piston.

In another version, the piston skirt is secured on the piston by appliedmoulding.

In a further version, the skirt is secured on the piston by adhesivebonding.

It is of course possible to reverse the structures, with the pistonhaving, for example, projecting elements that penetrate into aperturesformed in the piston skirt.

In another version, the piston skirt comes into abutment on a shoulderof the front and/or rear face of the piston.

It will be noted that the piston seal plays a part in the axialretention of the piston skirt on the piston, and that the constitutionof the piston in plastics material facilitates assembly of the pistonskirt with the piston.

In another version, an additional plastics member is associated with thepiston for trapping the piston skirt and holding it in position.

This additional member may for example be ultrasonically welded on thepiston so as to retain the piston skirt.

In a further version, the welding operation is carried out locally byindirect application of heat with the aid of at least one energy sourceof the laser type.

The supplementary member may be attached by conical telescopicengagement on the piston in order to trap the piston skirt in positionlocally.

Thus in these embodiments, the piston skirt is sandwiched locallybetween the piston, which is preferably of a plastics material, and theadditional member which is of plastics material.

In the case where the control cylinder is an emitter cylinder, thepiston skirt has at least one anterior hole which puts the hydraulicchamber into communication with a reservoir associated with the emittercylinder.

Preferably several holes are provided to ensure a higher flow of fluid,and to enable any orientation to be avoided during assembly, with a viewalways to having a passage in the upper part of the piston.

The position of the passage hole or holes is determined according to theaction of the piston skirt which is movable from one side to the otherof a secondary seal, such as a lip seal. It will be appreciated that noburr is formed at the outer periphery of the piston skirt, and thisfacilitates sliding of the latter within the cylinder body.

Preferably, the securing skirt has at least two posterior abutments,such as lugs or pegs, which are diametrically opposed to each other soas to cooperate with the piston skirt and limit the displacement of thelatter.

Thus the tolerance of the dead travel of the piston skirt is determinedby the aggregate of the tolerances of three components.

It is easily possible to incorporate an integral reservoir with theemitter cylinder.

This working cylinder can be formed by means of a bellows, or a sealedmembrane which is able to be unrolled, interposed operatively betweenthe cylinder body and the piston rod.

The membrane or the bellows has at each end a bead for fastening them onthe fixed part (that is to say the cylinder body) and on the movablepart (that is to say the piston rod).

Fastening members are secured, for example by snap-fitting, on the fixedpart and the moving part respectively in order to retain the beads.

Thus it is possible to return leaked fluid back into the workingreservoir, and the reservoir is defined by a flexible and elasticelement consisting of the bellows or membrane, which are typically ofelastomeric material such as rubber.

In addition, filling of the hydraulic control device for the clutch maynot have been carried out before it is fitted on the motor vehicle,filling then being carried out with the aid of the main reservoir. Thehydraulic control device can of course be filled beforehand.

In another version, the main reservoir may be omitted, and reliance thenplaced on the above mentioned integral reservoir only. In each case, thesecondary seal is submerged in the control fluid so that its usefulworking life is increased because it is not in contact with the air.

In one embodiment, a protective cap is provided and replaces the bellowsor the membrane. This cap surrounds the fastening skirt.

This cap is of plastics material and it includes a portion which definesan abutment and clipping means, such as lugs or pegs, for clipping thecap on the piston rod.

In another version, the cap is supported on the fixed part (that is tosay the cylinder body or the skirt) in the same way by clipping.

In a further version, the cap retains an elastomeric sealing member, onthe piston rod and the fixed part respectively.

In another version, the cap constitutes one of the members for fasteningthe bellows and/or the roll-out membrane.

The fastening skirt includes passages for giving communication with aworking reservoir and/or a main reservoir.

The skirt has at least one circumferential or axial groove for enablingfluid to pass freely.

The skirt is attached on the cylinder body for example by ultrasonicwelding, laser welding, friction welding or clipping, or by adhesivebonding or screw fastening.

Ultrasonic welding or laser type welding enable good sealing to beobtained and enable the number of seals to be reduced.

The cylinder body includes an aperture which can be closed by a plug.This aperture gives communication with the main reservoir.

In the case where, as mentioned above, an integral reservoir is enough,then the aperture is plugged. The plug is a component of the same natureas the cylinder body, being preferably of plastics material. The plug isfor example ultrasonically welded on the cylinder body, the said weldgiving sealing.

The fastening skirt has external mounting apertures which enable thepiston skirt to be centred with respect to the cylinder body during theoperation of welding by welding the skirt ultrasonically on the cylinderbody.

The mounting apertures serve for receiving a fitting tool havingprojections which penetrate into the mounting apertures, so as to beengaged with the piston skirt and also to grip the latter.

These apertures define a space around the piston. The mountingapertures, in one embodiment, consist of blind axial slots which areopen at the rear of the fastening and guiding skirt. In another version,they are oblong holes. These apertures are apertures that give access tothe piston skirt. Because of the simple tool used, accurate fitting isobtained. The said tool ensures that the various bores for guiding thepiston are coaxial and aligned with each other.

In another version, of course, instead of welding it is possible to useadhesive bonding.

The following description illustrates the invention with respect to theattached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in axial cross section of an emitter cylinder made inaccordance with the features of the invention, in which the piston isshown both in an advanced first position and in a retracted secondposition;

FIGS. 2 to 4 are views as seen in the direction of the arrows 2, 3 and 4respectively in FIG. 1,

FIGS. 5 and 6 are partial views of an enlarged scale showing,respectively, the front part and the rear part in FIG. 1;

FIG. 7 is a partial view taken from FIG. 6, showing the groove of thepiston for fixing the piston skirt of the piston;

FIGS. 8 to 10 are Figures which are similar to FIG. 1, but which showfurther embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In all of the drawings, those elements which are common will be giventhe same reference signs.

In FIGS. 1 and 8 to 10, a control cylinder is shown in the form of anemitter of a control apparatus for a motor vehicle clutch.

Such an apparatus (not shown) includes an emitter cylinder which isconnected through a duct to a receiver cylinder, the structure of whichis similar to that of the emitter cylinder.

Each cylinder, whether it is a receiver or an emitter, comprises apiston which is movable axially within a cylinder body for delimiting avariable volume hydraulic chamber. A connecting orifice, on which theduct is connected, is open into the hydraulic chamber.

The emitter cylinder includes a piston rod which is connected forexample to a clutch pedal operated by the driver, or an actuator whichis operated in accordance with predetermined programmes.

The piston of the emitter cylinder is adapted to expel a fluid, such asoil, which is contained in the hydraulic chamber, towards the pipe orduct which connects the emitter cylinder to the receiver cylinder.

When the clutch is engaged, the volume of the hydraulic chamber of theemitter cylinder is at a maximum, while the volume of the controlchamber of the receiver cylinder is at a minimum.

During operation of the clutch, the volume of the hydraulic chamber ofthe emitter cylinder diminishes, while the volume of the control chamberof the receiver cylinder increases.

The piston of the receiver cylinder then acts on a rod which itselfacts, for example, on the declutching fork that actuates the clutchrelease bearing which is part of the friction clutch.

Each one of the emitter and receiver cylinders includes a spring whichacts between the piston and the base of the body of the cylinder. Whenthe driver releases the clutch pedal, or when the actuator reverts toits initial clutch engaged position, the return spring of the emittercylinder expands in order to return the piston to its initial position,while the return spring of the emitter cylinder is compressed by theclutch spring, for example a diaphragm, which thus returns the piston ofthe receiver cylinder to its initial position.

In FIGS. 1 and 8 to 10, the emitter cylinder is shown in its deliveryposition, and it comprises a cylinder body 17 having an inlet port 18which is closed by a plug 19. It is through this inlet port that theduct or pipe which connects the receiver cylinder to the emittercylinder is open into the hydraulic chamber 20 of the emitter cylinder.

The chamber 20 is a variable volume chamber, and it is bounded by thebody 17, while the piston 21 is mounted for axial movement within thebody of the cylinder 17.

In the examples shown, the cylinder body 17 and the piston 21 are ofmouldable plastics material.

This plastics material is reinforced if required with glass fibre,Kevlar and so on, in order to give the required strength to thecomponents 17, 21.

The cylinder body 17 is of generally tubular form. The body 17 has aninternal bore 12, 23 of blind form, which is best seen in FIG. 5. Thebody 17 is in the form of an internally stepped tube having an axis ofaxial symmetry X—X (FIG. 1) with, at the front, a transverselyorientated base 24, into which the inlet port 18 of a connecting portion25 is open, permitting the above mentioned duct to be connected, forexample by clipping, the connecting portion 25 having for this purposeinternal passages, not given a reference numeral, through which a wireclip 48 is passed to connect the above mentioned duct to the emittercylinder. In another version, the connection is of the screw type. Thebody 17 is open at the back.

The connection 25 and the base 24 are part of the front part 26 of thecylinder body 17, while the open other end of the cylinder body is partof the rear part 27 of the said body.

The front part 26 has a diameter which is smaller than that of the rearpart 27, due to the fact that the body 17 is in the form of a steppedtube. The internal bore 22, 23 accordingly has a rear portion 23 whichis within the rear part 27 and which has a larger diameter than itsfront portion 22 which is within the front part 26.

Stiffening ribs may be provided on the front part 26 delimited by thebase 24.

The piston 21 is arranged to slide within the body 17, and moreprecisely in the internal bore 22, 23 of the latter, between an advanceor clutch engaging position, which is shown in the upper part of FIGS.1, 5, 6 and 8 to 10, and a retracted or declutching position which isshown in the lower part of FIGS. 1, 5, 6 and 8 to 10. In the retractedposition the chamber 20 and the control fluid are under pressure, whilein the advance position the chamber 20 and the control fluid aredepressurised.

It will be noted that a frusto-conical projecting element 28 is formedby moulding on the base 24.

The projecting element 28 extends axially, and its base perimeter servesto centre the return spring 29, which in this example is a helicalspring acting as described earlier herein between the body 17 and thepiston 21, and more precisely, here, between the transverse base 24 andthe front end of the piston 21.

The piston 21 has (see FIGS. 5 and 6) a transverse wall 30, the frontface 31 of which delimits the hydraulic chamber 20, with its rear face32 being in cooperation with the piston rod 33, which in this example isof metal.

The transverse wall 30 is extended forward by a chimney element 34 whichhas a frusto-conical external profile and a blind cylindrical centralhole 35.

The base of the hole 35, which is orientated axially, is defined by thefront face 31 of the wall 30.

The helical return spring 29 is mounted around the chimney element 34,the base of which serves to centre the return spring, the rear end ofwhich bears on the front face 31 of the transverse wall 30 of the piston21.

The spring 29 therefore works axially between the base 24 and the frontface 31. The port 18 does of course extend through the base 24 and isopen laterally with respect to the projecting element 28, which isformed by moulding so as to project from the base 24 and serving byvirtue of its base perimeter to centre the front end of the spring 29.

The end face 36 of the projecting element 28, in accordance with onefeature, acts as an abutment for the front face 37 of the chimneyelement 34.

More precisely, in the retracted position the piston 21 comes intocontact, through the front face 37 of the chimney element 34, with theend face 36 of the projecting element 28. The body 17 accordingly has anabutment, 28, which limits the forward displacement of the piston 21.

The chimney element 34, being arranged to come into contact with theprojecting element 28 which constitutes the above mentioned abutment, isrigid. The chimney element 34 stiffens the piston 21, which is made ofplastics material.

The transverse wall 30 is extended towards the rear by a sleeve portion38 which has an outwardly divergent bore 39.

In this example, the bore 39 is frusto-conical, its base being partlydefined by the rear face 32 of the transverse wall 30 of the piston 21.

The base of the bore 39 is hemispherical in general form, so as toreceive the head 40 of the rod 33 at its front end. The head 40 has thegeneral form of a spherical bore which penetrates into thecomplementary, generally hemispherical base of the internal bore 39 ofthe sleeve portion 38.

The said sleeve portion 38 is divided into axial fingers by slots, inaccordance with one feature.

The external form of the sleeve portion 38 is cylindrical, with anoutside diameter greater than that of the chimney element 34, the head40 of the rod 33 being arranged to spread the fingers of the sleeveportion 38 by contact with the internal bore, until it comes intocontact with the hemispherical portion of the base of the bore 39.

The rod 33 is accordingly mounted by a ball-type coupling in the piston21, and more particularly in the base of the sleeve portion 38 which isdivided into axial fingers by slots.

In accordance with one feature, the transverse wall 30, and thereforethe piston 21, carries at its outer periphery a piston seal 41.

In this example, the seal 41 is an O-ring seal fitted in a groove, notgiven a reference numeral, of the transverse wall 30 at its outerperiphery. The seal may take other forms.

The said seal 41 is arranged to cooperate, in accordance with onefeature, with the inner periphery of a metallic piston skirt 42. Thepiston skirt 42 surrounds the piston 21, and in this example it istubular in form. The piston 21 accordingly penetrates into the interiorof the skirt 42. In a manner to be described later herein, the rear endof the piston projects axially with respect to the rear face of theskirt 42.

The piston skirt 42 is for example of anodised aluminium material, ortreated steel. The piston skirt 42 projects axially forward with respectto the chimney element 34. In the retracted position, the chimneyelement 34 is in contact with the projecting element 28, while the skirt42 is spaced away from the base 24.

The piston chimney element 42 is spaced radially away from the chimneyelement 34 and return spring 29.

The said skirt 42 is in contact with the transverse wall 30 of thesleeve portion 38.

More precisely, the piston skirt 42 is in intimate contact at its innerperiphery with the outer periphery of the seal 41.

The seal 41 therefore immobilises the piston skirt 42 with a grippingaction.

The said skirt 42 tends to close off the sleeve portion 38. Moreprecisely, the skirt 42, by exerting a radial force, forces the fingersof the sleeve portion 38to become deformed radially inwards. Thus, thesleeve portion 38 is fitted in the skirt 42 in a prestressed condition.

Therefore, again, the sleeve portion 38 immobilises the piston sleeve 42with respect to the piston 21 with a gripping action.

The said skirt 42 is thus, in accordance with one feature, fixed axiallywith respect to the piston 21.

The said skirt is also fixed to the piston 21 for rotation with thelatter, by virtue of the seal 41 and sleeve portion 38.

In order to complete this axial immobilisation, and also to complete theimmobilisation against rotation of the skirt 42 with respect to thepiston 21, it is proposed that one of the elements consisting of thepiston skirt 42 and the piston 21 should have one or more lugspenetrating into one or more recesses formed in the other one of theelements consisting of the piston 21 and piston skirt 42.

For example, the skirt 42 may have at its rear end holes into whichthere penetrate radial projections in the form of lugs, which projectfrom the outer periphery of the sleeve portion 38 at the rear of thelatter. The skirt is therefore force-fitted over the outer periphery ofthe piston 21, until the radial projections of the sleeve portion 38penetrate into the holes of the skirt 42.

Thus the skirt 42 is snap-fitted on its piston 21.

In this example, as can be seen in FIG. 7, the rear end of the sleeveportion 38 has at its outer periphery a fastening groove 43, while therear end of the piston skirt 42 is deformed locally, radially inwards,so as to form lugs 44 which come into engagement with the rear flank andthe base of the fastening groove 43.

In another version, the rear end of the skirt 42 is formed with localteeth or has fingers to penetrate into the fastening groove 43.

In a further version, the rear end of the skirt is secured on the piston21 by in situ moulding.

Regardless of all this, in all cases a sub-assembly is formed consistingof the piston 21 and the piston skirt 42, to constitute a unit which ismovable axially in the body 17. The skirt 42 and the piston 21 arecomponents which are concentric and coaxial with each other.

The said piston skirt 42 prevents the fingers of the sleeve portion 38from being spread radially outwards, so that it locks the rod 33 axiallyin the interior of the piston 21 without any additional component. Therod 33 is therefore unable to escape axially from the piston 21, whileit remains able to rotate in three dimensions, by virtue of the seating1 38 (which in this example is generally hemispherical in form) of thesleeve portion 38, and the rear face 32. It is of course possible tocontrol the stress exerted by the piston skirt 42 on the sleeve portion38 in such a way that the piston rod 33 can be removed manually.

All of this is made possible because the piston is made of plasticsmaterial and because of the flexibility of the sleeve portion 38.

It is of course possible to secure the skirt 42 on the piston 21 byadhesive bonding, after the piston rod 33 has been introduced into thepiston. In all cases, the piston 21 is, in accordance with one featureof the invention, configured internally so as to receive the head 40 ofthe piston rod 33. The piston 21 has an internal seating for the head40. The seating is defined by the sleeve portion 38, which is flexiblebecause of its slots, and the rear face 32.

The said head 40 may, in this connection, take another form, and thesame is true for the interior of the sleeve portion 38 and seating.

The body 17 is adapted to be fixed on a fixed part of the vehicle, andis accordingly part of a fixed part of the emitter cylinder, while thepiston 21 and the piston rod 33 are part of the movable part of the saidcylinder.

For this purpose, the body 17 in this example has an integralintermediate plate 45 between the front part 26 and rear part 27 of thebody 17.

The plate 45 has two parallel edges which are joined together by twopointed lateral flanks.

The plate 45 is formed integrally by moulding with the front part 26 andrear part 27 of the body 17, and projects transversely with respect tothe tubular parts 26, 27. In this example the plate 45 has two fasteningears 46 which project radially with respect to the parts 26, 27.

These ears 46 have holes 47, through which there pass fastening members,usually screws, for fastening the body 17, and therefore the emittercylinder, to a fixed part of the motor vehicle.

In FIG. 3, the distances D and L show the distance between the axes ofthe holes 47 and the distance between the summits of the lateral flanksof the plate 45, respectively. Also, at 48, there can be seen the wireclip which is carried by the connector 25, and which serves for therapid clip fastening of the end of the above mentioned duct in theconnector 25.

A tube 49, fixed to the body 17, can also be seen in FIG. 3.

This tube 49 serves to connect the interior of the body 17 with a mainfeed reservoir which is mounted on the outside of the emitter cylinder,given that the hydraulic chambers of the emitter and receiver cylindersare filled with a hydraulic fluid which in this example is oil. Thereservoir is partially filled with this hydraulic fluid, and isconnected through a duct, not shown, to the tube 49 which is open intoan aperture 50 formed in the front of the plate 45 which is integral, bymoulding, with the body 17. The aperture 50 is connected to a duct 51extending through the plate 45 (FIG. 6). In this case several ducts 51are provided.

These ducts 51 are open at the front into a feed groove 52 which is incommunication with the aperture 50, while the ducts 51 are open at therear end, within the rear part 27 of the body 17, and more precisely inthe bore 23 of the rear part 27.

The aperture 50 is annular in form, and the tube 49 has at its base ashouldered ring portion 53 which is complementary to the aperture 50 andpenetrates into the latter, in such a way that the tube can be securedby sealed adhesive bonding to the plate 45.

In this example, fastening of the tube 49 to the plate 45 is obtained byinsertion of the ring portion 53 into the aperture 50, and then bymaking an ultrasonic weld between the annular edge of the aperture 50and the outer periphery of the ring portion 53.

To this end, the tube 49 is of course made of a plastics material whichis compatible with the body 17.

In all cases, whether adhesive bonding or ultrasonic welding is used, asealed fastening is obtained, without any additional seal, of the tube49 on the plate 45, the tube 49 being inclined with respect to the plate45. As a result of this, the ducts 51 and the groove 52 are easilyformed by moulding. In another version, the tube 49 is replaced, as canbe seen in FIG. 9, by a plug 149 which obturates the aperture 50, andwhich is secured by sealed adhesive bonding or sealed ultrasonic weldingto the plate 45, like the tube 49 in FIG. 6. The body 17 is accordinglystandardised.

In this example the interior of the tube is of stepped diameter, todefine three bores 22, 23 and 123.

In the manner described above, the bore 22 having the smallest diameteris formed in the front part 26 of the body 17, while the other two bores23, 123 are made, respectively, in the rear part 27 and in the plate 45of the body 17.

The bore 123 is formed centrally in the plate 45, and it has anintermediate diameter with respect to the bore 23 formed in the rearpart 27.

Because of the bores 23, 123, a fastening and guiding skirt 54 can befitted in the body 17. This skirt 54 is thicker than the piston skirt42. The skirt 54 is made of plastics material, and has an internal borethe diameter of which is equal to that of the bore 22 in the front partof the body 17. The skirt 54 is fixed to the body 17. Thus the saidskirt 54 is fixed, while the piston skirt 42 is movable axially.

The skirt 54 guides the piston skirt 42. More precisely, the innerperiphery of the skirt 54 of plastics material is in intimate contactwith the outer periphery of the metal piston skirt 42. The skirt 54 hasa stepped diameter externally, so that the said skirt 54 is fitted byinsertion into the rear part 27 and into the plate 45, the outerperiphery of the skirt being in cooperation with the inner periphery ofthe plate 45 and that of the rear part 27 of the body 17. The said skirt54 is therefore inserted in a complementary manner in the bores 123, 23.

The tubular skirt 54 has, integral with each other, a front portion 55,an intermediate portion 56 and a rear portion 57.

The front portion 55 is received in the complementary bore 123, whilethe portion 56 is received in the complementary bore 22.

After the skirt 54 has been inserted in the body 17, the skirt isfastened sealingly within the body by ultrasonic welding in the regionof the outer periphery of the portion 56 and the inner periphery of therear portion 27, as is indicated at 58 in FIG. 6.

In another version, the skirt 54 is sealingly attached by adhesivebonding on the body 17.

The intermediate portion 56 partly surrounds the rear portion 57, andthere is a large annular space between the portions 56 and 57.

The rear portion 57 has an outer diameter which is smaller than that ofthe front portion 55, the outer diameter of the latter being itselfsmaller than that of the intermediate portion 56. The portion 57 islonger in the axial direction than the portion 56 or 55, so as to givegood guidance to the movable skirt 42. The lengths of the portions 55,56 are a function of the length of the bores 23, 123.

Sealing of the hydraulic chamber 20 with respect to the outside isprovided by a dynamic seal 59 which is carried by the cylinder body 17,and which cooperates with the outer periphery of the piston skirt 42,that is to say with the cylindrical outer surface of the skirt 42.

The seal 59 is mounted within the bore 123, and is therefore in contactwith the inner periphery of the plate 45 which defines the bore 123. Theseal 59 is in axial contact with the front face of the front portion ofthe guide skirt 54, and with axial bosses 60 which are formed integrallyby moulding with the transverse shoulder 61 that joins the bore 22 tothe bore 123.

Thus the seal 59, which is a so-called secondary seal, makes a goodabutment on the bosses 60, and is preserved. In this connection, in thecase where the seal 59 is in contact with the shoulder 61, a deformationof the seal 59 occurs in the region of the radius joining the shoulder61 to the inner periphery of the plate 45. The seal 59 is a lip seal.The piston skirt 42 has at least one hole for providing communicationbetween the inside and the outside of the skirt 42.

This hole 62 is located as a function of the axial movement of thepiston 21 and skirt 42 on either side of the lip seal 59. Then, thishole 62, when the clutch is engaged, provides communication between thehydraulic control chamber 20 and the external main reservoir.

During actuation of the clutch, this communication is interruptedbecause the hole 62 is displaced on the other side of the seal 59.

In this example several holes 62 are provided in order to give a greaterflow of fluid and to prevent orientation during fitting.

The holes 62 are spaced apart at regular intervals.

It will be noted that the skirt 54 immobilises the seal 59 axially, sothat it constitutes an immobilizing skirt.

This skirt 54 has at its inner periphery at least one axial groove 63which is accordingly open in the region of the lip of the seal 59. Inthis example several axial grooves 63 are provided.

As can be seen in the upper part of FIGS. 5 and 6, in the advancedposition, with the clutch engaged, there is communication between thechamber 20 and the grooves 63 via the holes 62, the inclined lip of theseal 59 enabling such communication to exist. The holes 62 are adaptedto be displaced on either side of the second seal 59.

All of this enables communication to be obtained with the externalreservoir, and enables leaks to be recovered.

More precisely, the external reservoir is connected to the tube 49 incommunication with the aperture 50, the groove 52 and the internal bore23, via the ducts 51 which are open into a space bounded by thetransverse shoulder 64 joining the bore 123 to the bore 23, through thefront face of the intermediate portion 56, and through the outerperiphery of the portion 55 and the inner periphery of the rear portion27.

Passages 65 are formed axially in the intermediate portion 56 so as toput the fluid coming from the external reservoir into communication withthe annular space that exists between the portions 56, 57 and thegrooves 63 which have a closed base.

In order to avoid escape of the fluid outwards, a sealing bellows 66 isprovided, which is fitted between the rear portion 27 of the body 17 andthe rear of the piston rod 33. In this example, the liquid is able topass through the plate 45 and the fastening and guide sleeve 54, so asto reach the axial grooves 63 and to communicate with the chamber 20 viathe passage holes 62.

In accordance with one feature, the skirt 54 limits axial displacementin one direction of the unit consisting of the piston 21 and pistonskirt 42.

For this purpose, the fixed skirt 54 has at its rear end at least oneabutment 67 (FIG. 7), and in this example a plurality of abutments,orientated transversely and allowing fluid to pass. Thus, the pistonskirt 52 which is movable axially is able to come into contact, in theadvanced position, through its rear face with the abutments 67. The rearend of the piston 21 projects axially with respect to the rear end ofthe skirt 42, which is subjected to small forces when it is in contactwith the abutment 67, because the chamber 20 is depressurised.

It will be noted that there is fluid communication between the grooves63 and the space outside the skirt 54, because of the radial clearancethat exists between the piston 21 and the abutments 67.

The bellows 66, which in this example is of elastomeric material, has ateach of its ends transverse beads 68, 69 which are fixed, respectively,on the body 17 and on the piston rod 33, with the aid of fasteningmembers 70, 71 which in this example are of metal.

More precisely, the rear end of the rod 33 has two grooves 72, 73 whichare separated axially. The groove 72 is arranged to receive the bead 69,while the groove 73, which is the one furthest away from the body 17, isarranged to receive pads 74 of the tubular fastening member 71, as canbe best seen in FIG. 2. This member 71 consists of a collar piece ofstepped diameter (FIG. 2), with a continuous rear portion which isextended by a front portion 76 of larger diameter and divided by slotsinto radially elastically deformable lugs 77. The pads 74 are part ofthe lugs 77, and project inwards from the member 71.

Thus, the rear end of the bellows 66 is surrounded by the front portion76 of the component, being trapped between this portion 76 and the rod33, with the bead 69 being lodged within the groove 72.

The pads 74 penetrate into the groove 73 so as to locate the collarpiece 71 axially.

The member 70 is in the form of a collar piece with a base 77 whichextends generally radially.

Like the collar piece 71, the collar piece 70 has lugs 79 withdeformations 80 which are engaged in a groove (not given a referencenumeral) which is formed at the outer periphery of the rear part 27 ofthe body 17.

The bead 68 is trapped and gripped in a cavity which is bounded by therear face of the body 17, the outer periphery of the intermediateportion 56 and the base 78.

The bellows 66 is of stepped diameter, and comprises a rear part ofsmaller diameter which is adapted to come into engagement against therear face of the portion 57, and a front part of larger diameter whichsurrounds the portion 57. The rear and front parts of the bellows are ofaccordion form.

The portion 57 has external blind slots 83 for receiving a tool forfitting and centring the skirt 54. The slots 83 are open at the rear ofthe portion 57 and are closed at the front by the portion 56.

Thus the fitting tool surrounds and centres the portion 57, and itcentres the piston skirt 42 by virtue of projections extending throughthe slots 83 so as to come into engagement with the skirt 42.

It is thus possible to insert the assembly consisting of the skirt 54,the skirt 42 and the piston 21 in the body 17 and to proceed tofastening the skirt 54 to the body 17 by ultrasonic welding. It is ofcourse possible to replace the axially orientated blind slots 83 withoblong holes. In general terms, the rear portion has apertures forpassage of the projecting elements of the fitting tool.

The low cost of the hydraulic control device in accordance with theinvention, and its ease of assembly, will be appreciated.

In this connection, the skirt 42 is fitted over the piston 21.Similarly, the tube 49 and the skirt 54 are inserted respectively in theaperture 50 and the bores 23, 1 23.

The fastening members 70, 71 are fitted respectively over the portion 57and over the rod 33. The bellows 66, with the body 17 and the rod 33,defines an integral working reservoir. Ultrasonic welding between thebody 17 and the fixed skirt 54 gives sealing.

Thus, the emitter cylinder in accordance with the invention makes use ofa single dynamic seal, namely the seal 59, together with static seals,namely the seal 41 and the beads 68, 69 of the bellows 66. The seals 59and 41 are protected because they are submerged in the control fluid.

One dynamic seal is eliminated by virtue of the holes 62, grooves 63 andthe bellows 66 with its beads 68, 69.

In FIG. 1, the rear part of the bellows 66 is never fully compressed.The initial volume of fluid contained in this rear part is transferredinto the interior of the body 17 by the axial displacement of the piston21 It is then possible to omit the external main reservoir. This is whatis shown in FIG. 9, by virtue of the plug 149. It is of course necessaryto have regard to wear in the friction liners of the clutch in order toprovide the appropriate volume within the integral reservoir which isdefined by the bellows and which is interposed between the body 17 andthe rod 3. This reservoir therefore constitutes the only reservoir.

In FIG. 8, the rear part of the bellows 66 is fully compressed, so thatit is essential to provide an external reservoir, the working reservoirbeing no longer present.

Only the rear part of the bellows is of accordion form, the front partof the bellows being fitted over the portion 57.

It is of course possible to omit the bellows, as can be seen in FIG. 10.

In that case, a protective cap 1 66 is provided for giving resistance toshocks. The cap, which is of cylindrical form, surrounds the fixed skirt54 and is provided at its rear end with a base portion 1 67 which has acentral hole through which the piston rod passes. At its front end, thecap 166 has an annular radial flange 168 which extends outwards.

This flange 168 is fixed on the fixed skirt 54 by snap-fitting, which isobtained by means of a bead engaged in a groove in the body 17.

In this case the fixed skirt 54 only has an intermediate portion 56 anda rear portion 57.

The front portion of FIGS. 1 to 9 is replaced by a locating ring 155 inorder to enable a second dynamic seal 159 to be fitted between thelocating ring 155 and the portion 56, which is formed with a rebate inits inner periphery to accommodate the seal 159. The locating ring 155has radial grooves (not shown) at its rear end. The locating ring 155has internal axial grooves which replace the grooves 63 of FIGS. 1 to 9.Thus, liquid is in communication with the tube 49 through the holes 62.

In FIG. 10 the seal 159 is an additional seal which prevents leakage tothe outside.

The cap 166 can of course surround the bellows 66 of FIGS. 1 to 9. Forthis purpose, the fastening member 70 may be extended rearwards by atubular portion, at least partly surrounding the bellows. In anotherversion, the fastening member 71 is extended by a tubular portion at thefront for partly surrounding the bellows.

In a further version, the tube 49 and the fixed skirt 54 are of coursemounted in the body 17 by clip-fastening with the aid of an elastic wireclip fastener similar to the elastic clip 48, with passages for the clipbeing again provided, respectively, in the edge of the aperture 50 andin the rear part 27. In another version the members 49, 54 are fitted inthe body 17 by means of a mounting of the bayonet type.

In these variants, an additional seal must be provided.

The present invention is of course applicable to the receiver cylinder.

In all cases the piston skirt encloses the piston and forms asub-assembly with the latter.

The piston skirt 42 penetrates into the hydraulic chamber 20 and boundsthe latter. More precisely, the skirt 42 penetrates into the bore 22 ofthe front part 26; the bore 22 is extended axially by the internal boreof the fixed skirt 54, which can be referred to as the first skirt.

Because of the projecting element 28, the inlet port 18, whichconstitutes a connecting port, can in another version be open into thefront portion 26 between the base 24 and the piston skirt 42, havingregard to the fact that this skirt is spaced away from the base when thepiston 21 is in its retracted position.

The transverse wall 30 of the piston can of course be thicker, so thatthe seating 138 for receiving the head 40 of the rod 33 (FIG. 6) can beformed as a hollow in the transverse wall 30.

In the Figures shown, the seating 138 extends in cross section over alittle more than 180° so as to retain the rod 33 axially.

In another version, the seating 138 extends over 180° at least, and anattached ring, such as an open circlip, is attached in the piston 21 soas to locate the rod 33 axially.

This arrangement makes it possible to use a sleeve 38 which iscontinuous and rigid. The formation of a slotted sleeve 38 does ofcourse facilitate the fitting of the piston skirt 42 over the piston 21.

The piston 21 is located axially at its outer periphery on the pistonskirt 42, which can be referred to as the second skirt. For this axiallocation, the second skirt 42 may have a single lug, for example in theform of a bead which is engaged in a continuous groove of the piston,which in another version may be formed in the transverse wall 30 of thepiston 21.

A single lug and a single recess can therefore be provided on one of theelements consisting of the second skirt 42 and the piston 21.

The metal second skirt 42 is fixed at least axially to the piston 21,while the fixed first skirt 54 is fixed to the body 17, and is ofmouldable plastics material.

In FIGS. 1 to 9, a flexible element of elastic material defines areservoir which is incorporated in the emitter cylinder. This elementconsists of a bellows 66 made of an elastomer such as rubber.

The second skirt 42 slides axially in the first skirt 54, while the seal59 is in dynamic cooperation with the second skirt 42.

The chimney element 34 gives access to the outer periphery of the frontface 31 of the piston 21, while the sleeve portion 38 enables access tobe obtained to the central portion of the rear face 32.

The fastening members 70, 71 grippingly cover the ends of the flexibleelement of elastic material, which in this example is the bellows.

In FIG. 8 the base 78 of the fastening member 70 extends further inwardsin the radial direction.

In all the Figures, axial ribs, not given a reference numeral, join theportion 56, 57 radially together, while allowing the fluid coming fromthe external or internal reservoir to pass through.

In FIG. 10, the cap 166 for protecting the first skirt 54 is fixed onthe intermediate portion of the latter. The same can be true in FIGS. 1to 9. To this end, it is sufficient, firstly, to form a rebate in therear end of the intermediate portion 56 so that the bead 68 can befitted, and secondly, to make the groove for receiving the pads of themember 70 at the outer periphery of the portion 56.

It is of course possible to provide only a single pad on the members 70and 71, in the form of a bead.

The member 70 is fixed on one of the elements consisting of the cylinderbody 17 and the first skirt 54.

It then becomes possible to omit the ears 46 of the plate 45, and tofasten the cylinder body 17, using a bayonet fitting, on a fixed part inthe manner described in the document GB-A-1 539 879, to which referenceshould be made for more detail.

This fitting may of course be obtained using one of the portions 26, 27or the plate 45. The plate 45 can then be without any means forfastening it on a fixed part. The plate 45 is then able to be annular.

The apertures 83, which in this case are in the form of blind holes,formed in the rear portion 57 of the skirt 54, are openings givingaccess to the second skirt 42 so that the fitting tool can be engagedwith the second skirt 42, this tool being in engagement with the firstskirt 54. All combinations are possible.

In FIG. 8 the bellows 66 may consist only of a rear part of accordionform, fixed at the front on a protective cap surrounding the portion 57and attached sealingly on the rear portion 27.

The second skirt 54 and the tube can be attached by screw fastening onthe body 17.

The fastening member 71 may be replaced by a gripping collar. Thismember 71 can be fixed by seaming on the rod. The same is true for themember 70.

In another version, fastening of the member 70 is obtained with the aidof screws.

It is of course possible to replace the ultrasonic welds by means ofsealed spot welds by indirect application of heat using at least onesource of energy of the laser type. Radiation, in the form of a beamemitted by the laser, is for example in the infra-red radiation range.

One of the elements to be welded is of a material which is transparentto infra-red radiation, while the other one of these elements is soconfigured as to absorb this said radiation. For example, this otherelement is in material which is transparent to the said radiation andincludes at least one additive for absorbing the said radiation. Thisother element can of course be one that is absorbent to that radiation.

Thus, fastening of the tube 49 to the plate 45 can be obtained by thiswelding by indirect application of heat, giving sealed fastening. Thetube 49 is so configured as to absorb the said radiation, and is forexample of material transparent to the said radiation and having anadditive to make it transparent. The additive is for example in the formof pigments such as carbon in a proportion of 1 to 2%. It is thecomponent that is closest to the laser that is made of transparentmaterial, while the other is of absorbent material. Preferably, thelaser is turned with respect to the element to be welded. The inverse isof course possible. Thus the plate 45 is of transparent material.

This type of welding is more advantageous than ultrasonic welding,because it protects the seal 59 together with the components to bewelded, in such a way that the control cylinder is more reliable.Because of this, the ducts 51 and the groove 52 are easily made. Thesealed fastening at 58 can be obtained using welding by indirectapplication of heat.

The plug 149 may be secured using this type of welding.

Fastening of the skirt 54 in the body 17 can be effected by indirectapplication of heat, with the plate 45 being of material transparent tothe said radiation, while the other components to be welded are ofmaterial so configured as to absorb the said radiation.

In place of sealed ultrasonic welding, or welding by indirectapplication of heat, it is of course possible, for example at 58, tocarry out sealed friction welding and sealed high frequency welding. Inanother version, the sealed fastening is a fastening of the mirrorwelding type or the type in which ferromagnetic welds are made byinduction welding.

As will be clear from the description and drawings, the skirt 54, orso-called first skirt, and the piston are of plastics material, whilethe first skirt 54 has at least one abutment element 67 which is adaptedto cooperate with a rear end of the piston so as to limit the rearwardaxial displacement of the piston.

This abutment is arranged to cooperate with the rear end of the skirt 42which is called the second skirt.

In practice, the axial rear end of the first skirt has a plurality oftransversely orientated abutments which extend radially inwards. Theseabutments 67 are spaced apart angularly at regular intervals so as toenable fluid to pass through.

With this design for axial retention of the piston towards the rear,reduced tolerance is obtained in the value of the course of dead travelof the piston, in so far as it results from the aggregate of thetolerances of three components, that is to say the piston skirt 42, theexternal skirt 54 and the cylinder body.

In the embodiments described, the cylinder body 17 carries theintermediate plate, with which it is integral.

In another version the plate 45 is attached on the body 17.

Thus, the control device comprises the cylinder body 17, the skirt 54and a central member which is interposed between the cylinder body 17and the skirt 54. This components constitutes the plate 45. The dynamicseal is lodged within this intermediate member. The tube 49 is fixed onthe plate 45 and is connected to a transverse duct formed within theplate. This duct then opens into a central hole of the plate 45 facingthe external portion of the skirt 45. Two dynamic seals can then bemounted within the plate. This plate then includes housings for mountingdynamic seals of configurations similar to the seal 59. Fastening of theplate 45 on the body 17 is obtained in a manner similar to the fasteningof the skirt on the plate 45, that is to say using welding of the sametype as the weld 58, the plate 45 having a front portion similar to theportion 27 for the welding operation. The plate 45 does not serve forguiding the skirt 42, there being a radial clearance between the skirtand the contour of the hole in the plate, so that the duct connected tothe tube is able to open into a cavity closed by the two dynamic seals.It is the cylinder body and the skirt that guide the piston skirt 42.For more detail, reference should be made to the document FR 99.024.26filed on Feb. 26, 1999.

What is claimed is:
 1. A hydraulic control device for a clutch,especially for a motor vehicle, comprising at least one control cylinderhaving a first skirt (54), a cylinder body (17) having an anterior base(24) and open at the rear for receiving the first skirt (54) fastenedthereto, a piston (21) sliding axially in the cylinder body (17), apiston skirt (42) referred to as a second skirt, which is fixed axiallywith respect to the piston (21) and which slides axially in the firstskirt (54), a piston seal (41) carried by the piston (21), a second seal(41) carried by the cylinder body (17) for cooperation with the firstskirt (42), a piston rod (33) having an anterior head (40) forcooperating with the piston (21), wherein the cylinder body (17), thefirst skirt (54) and the piston (21) are of plastics material while thesecond skirt (42) is of metal, and wherein the piston (21) has a frontface (31) defining the hydraulic chamber (20) and a rear face (31)cooperating with the piston rod (33), wherein the piston (21) is soconfigured as to receive the head (40) of the piston rod (33) andsurrounded by the second skirt (42), and wherein the piston seal (41) isinterposed operatively between the outer periphery of the piston (21)and the inner periphery of the second skirt (42), which penetrates intothe hydraulic chamber (20), wherein the piston (21) has a transversewall (30) bounded by the front face (31) and rear face (32), and in thatthe transverse wall (30) is extended forward by a chimney element (34)and the base (24) of the cylinder body (17) carries an axiallyprojecting element (28) adapted to cooperate with the chimney element(34) to limit forward displacement of the piston (21).
 2. A deviceaccording to claim 1, wherein the transverse wall (30) is extendedrearward by a sleeve portion (38), into which the piston rod (33)penetrates, the sleeve portion (38) has an outer diameter greater thanthat of the chimney element.
 3. A device according to claim 2,whereinthe piston seal (41) is carried by the transverse wall.
 4. A deviceaccording to claim 2, wherein the end face (36) of the projectingelement (28) acts as an abutment for a front face (37) of the chimneyelement (34).
 5. A device according to claim 4, wherein the projectingelement (28) and the chimney element (34) are frusto-conical so as toserve for centring a return spring (29) which is interposed operativelybetween the base (24) of the cylinder body (17) and the front face (31)of the piston (21) and the return spring (29) is mounted around thechimney element (34).
 6. A device according to claim 2, characterized inthat the sleeve portion (38) is of split form and, with the transversewall (30), defines a seating (138) for receiving the head (40) of thepiston rod (33), and in that the second skirt (42) is fitted over thetransverse wall (30) of the sleeve portion (38).
 7. A device accordingto claim 1, characterized in that one of the elements consisting of thesecond skirt (42) and the piston (21) has at least one projectingelement that penetrates into a recess formed in the other one of theelements consisting of the piston (21) and the second skirt (42).
 8. Adevice according to claim 7, characterized in that the second skirt (42)has projecting elements, and in that the piston (21) has a groove (43)for receiving projecting elements of the second skirt (42).
 9. A deviceaccording to claim 8, characterized in that the projecting elementsconsist of deformations in the second skirt (42).
 10. A device accordingto claim 9, characterized in that the groove in the piston (21) isformed in a posterior sleeve portion (38) of the piston (21).
 11. Adevice according to claim 1, characterized in that the first skirt (54)has at its rear end at least one abutment (67) adapted to cooperate withthe rear end of the second skirt (42) so as to limit the displacement ofthe piston (21).
 12. A device according to claim 1, characterized inthat the second skirt (42) has at least one hole (62) for providingcommunication between the inside and the outside of the second skirt(42), and in that the hole (62) is adapted to be displaced on eitherside of the second seal (59).
 13. A device according to claim 12,characterized in that the second skirt (42) has at least one axialgroove (63) at its inner periphery.
 14. A device according to claim 1,characterized in that an integral reservoir is interposed operativelybetween the rear of the cylinder body (17) and the piston rod (33). 15.A device according to claim 14, characterized in that the integralreservoir is defined by a flexible element (66) of elastic material. 16.A device according to claim 15, characterized in that the flexibleelement of elastic material has, at both ends, beads (68, 69) by whichit is fixed, with the aid of respective fastening members (70, 71), onone of the elements consisting of the cylinder body (17) and the firstskirt (54), and on the piston rod (33).
 17. A device according to claim16, characterized in that the flexible element of resilient materialconsists of a bellows (66).
 18. A device according to claim 16,characterized in that the fastening member (71) fastening the element(66) of elastic material on the piston rod (33) includes projectingelements (74), and in that the piston rod (33) h as a first groove (73)and a second groove (72) respectively, for receiving the projectingelements (74) and for receiving the bead (69) of the flexible element ofplastics material, and in that the fastening member (71) overlies theflexible element of plastics material.
 19. A device according to claim14, characterized in that the cylinder body (17) includes anintermediate plate (45) between its front part (26) and its rear part(27), in that the plate has an anterior aperture (50), in that at leastone duct (51) extends through the plate (45) so as to connect theaperture to the bore (23) of the said rear part (27), and in that thefirst skirt (54) has holes for putting the duct (51) into communicationwith the integral reservoir interposed between the cylinder body (17)and the piston rod (33).
 20. A device according to claim 19,characterized in that the aperture (50) serves as a receptacle eitherfor a plug (149) or for a tube (49) adapted to be connected to anoutside reservoir.
 21. A device according to claim 1, characterized inthat the first skirt (54) is inserted in the cylinder body (17), beingfixed to the said body (17) with a sealed fastening such as anultrasonic weld or an adhesive bond.
 22. A device according to claim 1,characterized in that the first skirt (54) has external apertures forgiving access to the second skirt (51).